Objective:To compare the responses of angiotensin II (Ang II) and blood pressure to the renin inhibitor Ro 42-5892 and the angiotensin converting enzyme (ACE) inhibitor enalaprilSubjects:Eight non-sodium-restricted patients with mild-to-moderate essential hypertensionDesign:A single-blind crossover study. Ro 42-5892 (600 mg orally, once a day) and enalapril (20 mg orally, once a day) were given for 8 days before detailed investigations were carried out.Methods:Ambulatory blood pressure was measured directly for 24 h by the Oxford technique on three occasions. Off-treatment and on day 8 of treatment with Ro 42-5892 and with enalapril. Ang II was measured by radioimmunoassay after separation by high-performance liquid chromatographyResults:Plasma renin activity and Ang II were lowered by 83% [95% confidence interval (CD 61-105] and 68% (95% Cl 49-87), respectively, 0.5-1 h after Ro 42-5892, but after only 3h values had returned to baseline. Unlike this rapid and short-term suppression of Ang II, the maximal antihypertensive response to Ro 42-5892 (fall in blood pressure 12.9/9.0 mmHg) occurred only after 6h. Blood pressure returned to baseline after 8h. In response to enalapril, Ang II was maximally suppressed by 63% (95% Cl 32-94) after 2 h and by 83% (95% Cl 76-90) after 8 h. Despite early maximal Ang II suppression, the maximal antihypertensive response to enalapril occurred only after 12 h (fall in blood pressure 25.3/16.3 mmHg). With this compound a significant antihypertensive effect was still present 24 h after dosing.Conclusions:Compared with enalapril at 20 mg once a day, repeated oral administration of a single dose of Ro 42-5892 at 600 mg caused only short-term suppression of Ang II and blood pressure. Suppression of Ang II and reduction in blood pressure were temporally dissociated, both with the ACE inhibitor and the renin inhibitor. This implies that the blood pressure lowering effect of these inhibitors is caused partly by Ang II suppression outside the circulation